Let me know if you have any questions about electrical theory or installation, or anything else!
I do quite a bit of DIY electrical in my home, both because I enjoy tinkering and because I live in a developing country where most of the electricians you can hire is better described as "practiced amateur" rather than "professional," and I've gotten by with online resources (and the fact that my house is made from non-combustible materials) but as you point out in that post, there's a lot of conflicting or downright wrong information.
I don't want to become an actual electrician, but aside from just being interested in the topic, I'd at least want to know for sure that what I'm doing is safe and to be able to check the work of anyone I hire for obvious faults. I'm planning a solar installation in the near future, so I'd like to be well informed on how everything is supposed to work.
I would be interested in your comments about that article, thanks!
Also misconceptions about electricity taught in school:
Or pages on generally believed science myths:
How transistors really work:
How capacitors really work:
There's loads more great stuff. He's a pleasure to read - a guy who thinks for himself, and experiments - tries things out for himself.
The neutral line is connected to Earth at some point. The voltage difference is created by a transformer upstream which just pushes a 240V (or whatever) difference between live and neutral, and since neutral is tied to Earth, it stays at ~0V while the live line stays at ~240VAC.
You're right, though, that any current pulled from the live line goes back through the neutral line and they both end up with alternating current going through them.
The voltage only alternates between live (or 'hot') and neutral relative to each other. This voltage difference between the two lines is generated by a transformer and there doesn't have to be any connection between live/neutral and anything else (at which point you can just think of them as live-1 and live-2) but the neutral line is connected to Earth at some point (although depending on load and the distance to the earthing point your neutral will actually have some AC ripple on it).
If you have ever made the mistake of connecting a diode rectifier directly to AC mains, then grounding the negative output, you’ll blow a breaker. A 1:1 isolation transformer is still needed.
The only nit I'd pick is with the bit at the end about AC. The voltage on the neutral wire isn't due to inductive coupling, it's due to voltage drop along the neutral since neutral carries the same current as live. You'll always get this if anything's pulling significant current, earthing can't completely fix it, which is why you can't ever depend on neutral being the same voltage as earth, or as another neutral elsewhere (that's why we use dry contact relays to send signals between different pieces of kit - if they're getting neutral from different places then you can have a significant voltage difference between "neutral" in one cabinet and "neutral" in another, enough to blow up ELV gear!)
There's also the fact that, any time you use a transformer and don't earth both sides, you end up with a 'floating' AC circuit that will end up at some arbitrary voltage compared with earth. I've made this mistake before and been bitten by a stray (high impedance) 50VAC, not deadly but enough to get your attention. :P
I then plugged the trailer into an outlet on the side of the house so I could run the air conditioner while I packed it. There was an issue with the brake lights not always working on trailer also. I crawled under the truck to trace the wires (they had been spliced under there before so I wanted to check that area first).
While on my back I rested my forearm against the frame of the truck and then felt a small "pinch". I thought a bug bit me at first, but seeing nothing there, I touched my forearm back again to the frame and felt it again. I realized it was electricity. I had a multi meter handy and I stuck one end of the probe in my mouth and touched the other end to the frame. It read 50 volts a/c. I went and unplugged the trailer from the outdoor outlet and ran it through a window and plugged it into an outlet inside and the issue went away.
So what's up with that?
Usually 50 VAC means the ground is open.
A thing about most ordinary transformers is they wrap the primary and secondary together. Fast, cheap, and more efficient. The result is there is a large amount of capacitive coupling between the primary and secondary. Since one side of the secondary is grounded it's like connecting 1000-5000pf between hot and chassis ground. If chassis isn't grounded then it floats at 60VAC.
 For transformers with more isolation they wrap the primary and secondary on top of each other. Less capacitance that way. Medical grade transformers have physically separate windings.
With this said, having multiple point of load converters may have impacts on efficiency and will add to the cost of the system.
Your green wire would be what the US calls a ground wire, and what is more accurately called a Equipment Grounding Conductor (EGC). It's purpose is to bond all normally non-current carrying conductive parts of a system together to provide a ground-fault current path back to the source so that the overcurrent protective device can operate properly to open the circuit in the case of a ground fault. It is 100% a safety measure, and will operate as intended to open a breaker whether or not it is connected to the Earth.
Your red and black wires are both ungrounded conductors, and are the conductors which actually create the circuit that allows current to flow to power whatever you connect to the circuit. The circuit will work to provide current without the green wire. However, without the green wire, if either the red or black shorts to something, the breaker will not open and you have an enormous potential to harm someone or burn your house down.
This is not true. First of all only the red is hot, if the black shorts to something nothing will happen.
Second if there is a short strong enough to "burn your house down", the breaker most definitely will open.
I am correct on the EGC, though. It works the same as the EGC in the US. If a ground fault causes a house to burn down, then the breaker will absolutely NOT open. That's how the fire starts: current flows through something it shouldn't long enough to heat it up to the point that something ignites. If the breaker opens, the fire wouldn't have started in the first place.
By having a separate ground, it's harder to mess that up, and devices can connect the body of the device to that.
Inside the electrical box (mains) the neutral and ground are connected together, and are at the same potential.
The only reason they run separate wires is in case of of mistakes.
1. In case the neutral gets disconnected, so the frame isn't at the potential of the hot (no voltage drop across the device)
2. So the return voltage drop in the white wire isn't on the body of the device. ~20 volts between adjacent high-current appliances on different phases probably wouldn't be terribly dangerous to most people, but it is sloppy.
3. For GFCI/RCD, it separates bona fide return currents from "accidental" return currents. With only two wires, dropping a toaster into a (PVC-drain) bathtub wouldn't trip. (Erm, I just realized most toasters are actually only two wires. Well uh, don't do that).
The geometry of the electric field in water should probably be similar to that in air (mostly contained to within the case), just don't drop both a toaster and a waffle maker in at separate ends.
It assumes that any dangerous shocking current will be taking a path that isn't just coming back on its own white wire, presumably from taking an unspecified path to ground. This seems a reasonable assumption for safety (and the NFPA surely has looked at the data), but it doesn't really inform the above isolated-bathtub situation.
If the green wire is connected between the receptacle and the outlet/switch then it’s “bonding” the two mental items. (Using the terminology from post). Most people refer to this as the ground wire or grounding the receptacle. The purpose, from my understanding, is to have a stable system. In the event the hot wire touches the receptacle.
If the red/blue/green are coming from the same cable (3 wires inside another sheath), then your green is the ground/neutral that connects to the electrical box itself, while the other two are hot/lead.
I posted a similar question above which may clarify things if the OP answers.
Or can you elaborate but the meaning that it's trying to get back to it's source?
The electrical potential between any two given points is dependent on the impedance along the pathway between the two. The lower the impedance, the lower the potential (or work/energy needed to move current). So, yes, in a way electricity wants to get to the point with the lowest potential, but that point will always be the point where the electricity originates.
I was a little vague with "where the electricity originates" because that could be a number of things. It could be a battery, a transformer, a generator, a turbine, a dynamo, etc. Whatever is creating the difference in potential between two points is the "source" of the electricity.
It provides a nice visual for why current always makes it back to ground, just like water always flow downhill. It also removes the tendency to anthropomorphize electrical current and say things like it "seeks out" ground. When something falls from the sky we don't say it's trying to find the ground!
It's more like pipes full of a gas like air. The power plant has a big reciprocating piston that is pushing and pulling on the gas, creating a pressure wave. One side of the cylinder is "aired," meaning it is in contact with atmospheric air. These pipes make their way to clients, who attach the pipes to equipment of their own, for example a piston that converts this wave back into mechanical energy. Again, one side of this piston is in contact with atmospheric air, which is the reference pressure for the piston.
Sometimes the pipe develops small holes, and if a hapless worker gets too close, they can either get cut from an out-blast or hurt from smashing against the equipment when the air is sucking in (both being from the difference in the pipe's pressure relative to atmospheric pressure). As a safety protection, everything is enclosed in another layer of air-proof material, and when a leak is detected the main air supply is shut off.
Special attention is made to make sure the average pressure in the pipe is the same as atmospheric pressure, since the piston motors depend on this to function.
(In real life, steam plants use direct current since there are a lot of losses due to condensation, and also since a lot of the point is transmitting thermal energy.)
Yes, sadly, you are wrong. But it's not a strange error.
Electricity always flows in a circle(circuit).
And, in fact, in medical devices, transformers are often used to completely isolate devices from the line that they are plugged into. Electrons on the device side of the transformer will NOT try to flow back into the line side or an earth. They only want to flow back to the device side of the transformer.
Now, the issue is that when you want to create really strict isolation like this, suddenly all manner of things that normally you don't pay attention to suddenly become relevant. Is the device side of that transformer really not connected to the line side anywhere? No goop on the board? No water vapor? No lines that are a little too close? Is the hospital bed not connected to anything?
Guitar players who use tube amps and vocalists who use condenser microphones wind up with this issue all the time. Both the amps and the mics are "isolated" with relatively high voltage signals floating around--300-400V for amps:48V for mics--and consequently strange paths cause lots of "buzz" in the signal.
For example, the current into one terminal of a capacitor does equal the current out of the other terminal. Yes electrons are building up on one plate, but they're being depleted from the other - the net charge of the capacitor remains zero. If this weren't true, differently-charged capacitors would be physically attracted to one another!
If this goes against your intuition, it's because you've become so accustomed to this abstraction of ground which (mostly) lets you forget about the current flow on the other leg of the capacitor.
(In the electronics realm, the use of the term "ground" is much more casual compared to the NEC. To put it in terms of OP, "ground" in the electronics realm is more akin to the "grounded conductor", but alas could actually refer to anything you feel like thinking of as the reference.)
The realm of electrodynamics is pretty interesting, and it's where seemingly basic concepts like electric potential begin to fail -- it becomes path-dependent!
Not really. The problem is that we have sort of an "electron abstraction" which is incorrect in the Heaviside-Hertz pedagogy when fields start to store energy. I recommend "Collective Electrodynamics" by Carver Mead as a modern formulation without the silliness of an Aether:
> I only brought up ground (in the Earth ground sense) because I've heard people think that antennas in general work by using the Earth as a second conductor, with EM radiation as the first.
Really? Most of the time I describe antennas as sort of really long range transformers. And, while you need each side of the transformer to be a circuit, the two sides of the transformer don't have to interact other than through a field.
> My previous comment was written out of a reasonably common conception of a closed circuit being a loop with constant current flow, but capacitors break such a circuit.
Yes and no. Capacitors have the hand wavy notion of "displacement current" in classical electrodynamics--but most of the issue is with the fact that we use the Heaviside-Hertz pedagogy which was formulated back when everybody believed in the Aether.
The real issue is that to deal with capacitors you must deal with fields rather than just the notion of electrons. However, if we kind of squint and wave our hands the "electron formulation" can be kinda sorta made to work. (Side note: Capacitive dividers are even more annoying and you have to be really careful.)
Classical Heaviside-Hertz electrodynamics also has a lot of issues dealing with motors and generators, as well. Again, the key is that an "electron formulation" isn't really enough when fields start holding an appreciable amount of energy.
(Re "not really": with Maxwell's equations, the curl of the electric field is generally non-zero, so scalar potentials are not well-defined, which is all I meant. My experience is having gone through Purcell long ago, and by now I have some familiarity with [mathematical] gauge theory, but really I'm only an E&M dilettante.)
Essentially, the ground rod acts as an "anchor" holding the neutral wire and the ground at the same electric potential. If there was no ground rod, the earth and the circuit would be "floating" relative to one another, and a dangerously large voltage could develop between them.
What a voltage does is pull or push the charge carriers. When lots of them flow, you have a current. Conductors, like a wire or ground rod, are full of free electrons to act like charge carriers (kind of like a pipe filled with water, the voltage is a pump that moves it).
The duality of pulling/pushing charge carriers is why we need a circuit. In order to push charge carriers, we need something to pull them from (a source) and somewhere to dump them (a sink). When we have no source and no sink, charge carriers have nowhere to come from and nowhere to go.
Ground is a convenient source/sink for charge carriers because it's roughly uniform in charge and huge, so pulling tons of charge carriers from it doesn't impact it greatly.
And it's not that charge carriers are always flowing back to earth, but back to their source. That's why ground is sometimes called a "return path." To move a charge carrier, you need to give it potential. It will lose that potential and return to the point of lowest potential difference from its origin - which is its origin.
But that said, for things like AC power, the charge carriers aren't actually moving very far at all and have a net displacement of 0. They vibrate adjacent charge carriers, and we convert that vibration into unidirectional (DC) voltages that can push/pull from local sources/sinks, be it the literal earth (mostly for safety ground) or a small plane of copper on a PCB.
> And it's not that charge carriers are always flowing back to earth, but back to their source. That's why ground is sometimes called a "return path." To move a charge carrier, you need to give it potential. It will lose that potential and return to the point of lowest potential difference from its origin - which is its origin.
The neutral lines of circuits are often tied into Earth, making the voltages of the neutral line and the earth equal to one another at what we've defined to be 0V (for reasons of convenience and safety). There's no intrinsic property of Earth that gives it a low electric potential, and electricity doesn't intrinsically want to flow back into Earth.
Some training videos for pro electricians and US National Electric Code compliance helped me.
Basically, bond everything together if it can carry a charge. Ground that bond at only one place in an electrical service.
More than one "ground" sets up a situation where a potential difference can develop between the various "grounds". Ground Fault detection may no longer work in that case. Which is not good.
(The presentation is weirdly sexist in offhand comments, which I often encounter in trade work of this kind, but I do believe that's changing. Slowly. The USA needs more people who know how to build things.)
USA? The WORLD needs more people who know how to build things.
But don't worry, they'll teach you this special term "bonding" that refers to the latter. Except it doesn't. I already used a synonym of "bonding" - "hooking up". You "bond" the black wire to the gold terminal on a receptacle by tightening the screw.
> Basically, bond everything together if it can carry a charge
It is perfectly fine to say that you are grounding those things together. Connecting something to an EGC is indeed "grounding it" - just not in NEC land which is focused on getting the EGC grounded. If you say "this washing machine needs to be better grounded", that doesn't mean it needs an immediate connection to earth, but is rather talking about its path to earth via the building's electrical system.
This is incorrect (probably a typo) - the GFC ensures there is a very low resistance path to source, which ensures a current spike that is sufficient to blow the fuse.
It's perfectly okay to ensure your text is communicating accurate information - in fact leaving it may undermine your explanation as certain folks will focus on the error (or others won't notice it and learn something incorrect).
For example for UK, EU and NZ etc: sockets and pins have a variety of features to avoid touching the phase (live) wire with say a screwdriver or knife in hands of a child.
For example, all new circuits installed in New Zealand since 209 must have an Residual Current Detector (the actual rules lead to multiple RCDs per main power board). This will cut the circuit if someone does manage to touch a live wire somehow (current from phase to neutral doesn't match, because some of it is grounded through your body, and the mismatch triggers the breaker. Wayyyyyyy safer than a fuse!
I don't think I have ever seen a US plug where the pins have a non-conductive protective covering at the base of the pin (I think all modern UK and NZ male plugs have that. Although I'll be honest that I think the NZ solution makes plugs less safe due to risk of pins bending then breaking and leaving a live metal pin exposed in the socket).
EU sockets are mostly recessed from what I have seen (some NZ sockets are, but the recess is still is often unusable with old plugs, so is not common yet, but will become so as more plugs are sold that fit properly).
No, bad design is why they are caltrops. Over here in the Netherlands shutters are similarly required but none of our plugs need a third pin. The shutter is a see-saw construction that works in such a way that you need to insert both prongs at the same time for the shutter to rotate out of the way.
That said our grounded plugs are still caltrops for no real good reason, though less so than the UK ones. They tend to fall with the prongs to the side instead of prongs-up.
Its required by current US NEC code but older house are grandfathered in unless they do major renovation. Also some exceptions like outlets high enough to be out of reach of kids.
Its possible that the UK/NZ plugs have better designs. The code improves step by step here.
That is, if the hot wire touches a metal part of the fan which is not supposed to be energized (say the metal housing), and the fan is not properly bonded, then there will be no ground-fault path back to the source to cause the breaker to trip. This could mean that the housing of your fan would be energized with (in a home in the US) 120V, and would shock anyone who touches it.
First, NEVER work anything hot. There is no such thing as a safe voltage to work energized. Even a simple home receptacle circuit can easily kill you (and it happens with alarming regularity).
That said, ALWAYS work something AS IF it were hot (for the exact reason you said, accidents happen). This means connecting the safety measures first. The safest order to connect wires is: ground, neutral, hot. The safest order to disconnect wires is the opposite: hot, neutral, ground.
Half right, half wrong. It would not short if it touched the metal box, and would not trip the breaker. That part is right.
However if it touched YOU not having the ground wire connected actually helps you. It means the electricity does not have as a good of a path back to the box, and you'll get a weaker shock.
With the ground wire you'll get a much higher shock, but it won't trip the breaker!! Humans have too high resistance to trip breakers, you'll just keep getting shocked.
So it's kind of a wash - with the ground, it's more likely to just short against the box and trip.
Best is just to always wire things as if they are live. Only touch the wire if you have to, always use insulated tools, even if the power is off.
If that guy was connected to the earth he would get fried. Note that you still have to equalize whatever potential there is between you and the system, like they do in that video. Same reason why you should ground yourself and the hardware before working on your PC. Ever had a tiny spark hit you when you touched something (neither you or that "thing" being connected to the electrical grid, just static electricity e.g. from walking on the carpet)? But without connection to ground the only thing that happens is equalization of the potential between you and the target but no further flow. If you are connected to ground on one side and to a source that keeps creating an electrical potential, like the electrical grid with a power plant somewhere, there will be a continuing flow. If you are not connected to ground there won't be.
> Marvelous explanation.
It might be Marvelous, but it's not actually true. The ground wire IS connected to the earth!
I don't want to be rude, but I think the OP should take this post down, it has a LOT of mistakes.
The neutral bus is either bonded to the case with a green grounding screw or is integral with the ground bus.
Also, be aware of grounding requirements when using a generator:
Also, for home owners, what’s the best resource to learn common sense basics of electrical work (besides reading the city/states codes). Are there classes for such cases?
As far as learning common electrical, I'm sure local organizations in your area will have some kind of classes. Probably local hardware stores? I don't know. I learned through trade school and on-the-job training. As an electrician, I will self-servingly tell you that you should always hire a licensed electrician.
This is NOT TRUE!! You've said it so many times in this thread, and it's just not true.
A lot of people are tying to correct your mistakes, but you're not fixing them. Please do so, you are misleading a lot of people.
For 240V, can use 3-wire circuits by getting 240V between the +120V and -120V legs. There are 3-wire grounded plugs (hot-hot-ground) and non-grounded (hot-hot-neutral). Modern 240V wiring uses 4 wires, hot-hot-neutral-ground, which allows making 120V for low-power electronics from one hot to neutral.
"The ONLY purpose for the EGC (or green wire) is to clear a ground-fault (clearing a ground-fault means tripping a breaker or blowing a fuse) in the 'oh shit moments'. It has absolutely NOTHING to do with the ground or the Earth and will work exactly as it is intended to regardless of whether it is connected to the Earth or not."
If the EGC is floating, no current will flow in a ground fault and the breaker never trips.
The entire purpose of the EGC is to bond all normally non-current carrying conductive parts together to provide a ground-fault current path back to the source of the circuit. If the EGC is not connected to some non-current carrying conductive part, then it is not installed correctly, is against code, and is a safety hazard. If the EGC is bonded to everything properly and there is a fault (say an ungrounded wire touches a metal box), then the current will flow through the ungrounded conductor, through the metal box, through the EGC (which is bonded to the box), back to the source (usually a transformer), across the windings, and eventually back to the breaker that controls the circuit. This will build up enough current (usually VERY fast, like milliseconds) and the breaker will open. The Earth has nothing to do with this.
Also the EGC does have more purposes than simply clearing fault current - for example carrying away leakage current from the chassis of something with a switching power supply where the output can't be completely isolated to meet emissions. Ever been shocked by a laptop with only a two-prong AC adapter?
IMO this whole subject is a minefield of disagreements due to terminology, when really all questions are answered by drawing out the schematic of a typical electrical system and looking at the loops (circuits). For instance in the typical ground fault, the fault current returns to the distribution transformer in parallel through all of: your service's neutral, your grounding rod, your neighbors grounding rods/service neutrals, and your other leg of the split phase via turned-on devices. This seems like a lot of unrelated details to memorize until one draws it out.
EGC is bonded to the panel enclosure at the ground bus. The neutral bus is also bonded to the enclosure with a ground screw. So, the EGC is directly connected to the neutral bus and a fault between hot and a bonded enclosure is routed via the EGC to neutral, tripping the breaker.
If you don't bond neutral and ground at the main, it's still bound at the transformer.
> then the current will flow through the ungrounded conductor,
No, it will flow through the grounded conductor.
> back to the source (usually a transformer), across the windings, and eventually back to the breaker that controls the circuit
The flow of power is the same via ground as it is via neutral.
> This will build up enough current (usually VERY fast, like milliseconds)
There is no such thing as "build up enough current", current does not "build up".
The milliseconds has to do with built in time delays at breakers, it's not a function of the electricity.
> The Earth has nothing to do with this
The actual Earth is used as a conductor, so yes, it definitely has something to do with this.
That would be a pretty good trick. The transformer is outside my house on a pole. Two wires run to it, the hot and the neutral. The "ground" doesn't leave the house. (Other wiring schemes exist, but this is standard USA residential.)
[EDIT: brainfart, see helpful correction below. still no "ground" at the pole...]
Yes there is. The neutral is bonded to ground, via an actual metal pole in the ground.
In your house is the same thing: The neutral (and the ground) and attached to a metal pole in the ground.
And the earth itself completes the circuit.
Standard US residential is 240V split phase, with two hot and one neutral conductor from the transformer. So three wires, minimum. Unless you have a very old feed.
I've seen houses where the earth wiring is completely independent and terminated in a metal rod buried outside. Seemed to be up to local code, breakers worked as they should.
The MBJ/SBJ is what bonds the neutral. This doesn't have anything to do with the Earth. This bonding has to be done anywhere between the origination of the circuit and the first overcurrent protective device.
The GEC is what connects to the Earth. This is used to stabilize voltage and to eliminate a difference in potential between metal parts during a high frequency event (like a nearby lightning strike or a transformer blowing up). This has nothing to do with the operation of breakers.
Edit to clarify: In principle, only the voltage difference between Live and Neutral matters for running a device. So theoretically one could construct a building supply where Neutral is not at earth potential. However, EGC has to be at earth potential, otherwise there would be a voltage between any metal electronic device and earthed objects, such as radiators or your feet standing in a puddle. This means that in practice both Neutral and EGC are always physically connected to the earth in some way and have to be for the system to work properly.